In hydraulic braking systems for aircraft, the delivery of hydraulic power is controlled via a hydraulic shutoff valve. More particularly, the shutoff valve includes an inlet for receiving pressurized hydraulic fluid, and an outlet for delivering the pressurized hydraulic fluid. The outlet is typically coupled to control valves (e.g., servo valves) that control the actual pressure applied to a brake assembly.
If the shutoff valve is open, then hydraulic pressure is provided to the respective servo valves, and braking operation is enabled. If the shutoff valve is closed, however, the pressurized hydraulic fluid cannot reach the servo valves. Without hydraulic pressure at the servo valves, braking is inhibited.
In electric brake systems, electric power is provided to an actuator via an electromechanical actuator controller (EMAC). The EMAC delivers the electric current that is used by the brake actuator (e.g., a motor), which in turn provides a mechanical force on the brake disk stack.
If the EMAC is active (e.g., enabled and electrically coupled to the actuator), then electrical power can be provided to the actuator. Conversely, if the EMAC is not enabled, or not electrically coupled to the actuator, then electrical power cannot be delivered to the actuator and, thus braking is not possible.